( Reaffirmed 2000 ) Indian Standard HYDROPOWERINTAKES-CRITERIA FORHYDRAULICDESIGN (First Revision ) UDC 627.8404 : 621.22 8 BIS 1995 BUREAU MANAK OF BHAVAN, INDIAN 9 BAHADUR STANDARDS SHAH ZAFAR MARG NEW DELHI 110002 July 1995 Price &ap 7 Intake Structures Sectional Committee, RVD 11 FOREWORD This Indian Standard ( First Revision ) was adopted by the Bureau of Indian Standards, after the draft finalized by the Intake Structures Sectional Committee had been approved by the River Valley Division Council. An intake is provided in a hydroelectric development The intake design should be such as to: a) b) c) d) to let water into the water conductor system. Give minimum hydraulic losses; Prevent formation of air entraining vortices; Minimise sediment entry, specially in the case of run-of-the-river schemes; and Prevent ice and floating material from entering the conduit or penstock. This standard was first published in 1981. This revision has been prepared to incorporate certain changes necessitated in view of comments received from user organizations based on their experience in the use of the standard. The salient changes that have been incorporated in this revision are listed below: i) Additional information has been laid down for run-of-the-river type intakes. ii) Intakes in concrete and masonry dam has been divided in two parts and figures depicting semi-circular as well as penstock re-entrant type intake have been incorporated. iii) Intakes in reservoir independent of dam have been illustrated. iv) Layout of intake structures have been elaborated to include antivortex devices such as perforated breast-walls. v) Details of side flaring entry have been incorporated as an illustration. For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with IS 2 : 1960 `Rules for rounding off numerical values ( revised )`. The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard. IS 9761 : 1995 Indian Standard HYDROPOWERINTAKES-CRITERIA FORHYDRAULICDESIGN / d;i'rstRevision 1 SCOPE This standard describes the criteria for hydraulit design of hydropower intake structures. 2 TYPES AND CHOICE 2.1 J Type Intake 2.2 Run-of-the-River OF INTAKES 2.2.1 Run-of-the-river type intakes are those which draw water from the fresh continuous river inflows without any appreciable pondage upstream of the diversion structure. 2.2.1.1 barrages The position and location of intake would generally depend upon the type of development and may be broadly classified as under: Intake adjacent to diversion dams and a) Run-of-the-river b) Reservoir type intakes, and type intakes. / IN'IAKE In a Run-of-the-river type development without any appreciable pondage, an intake for tunnel is placed upstream of diversion dam or barrage. A typical detail is shown in Fig. I. SECTION e A-A Sk1 EXCLUDE SECTION B-B FIG. 1 INUKB AT BARRAGE 1 IS 9761 : 1995 2.2.1.2 Canal/river powerhouses intakes as forebay and intake for penstocks A powerhouse with short intakes as a part of powerhouse structure is located across large canals or rivers to utilise head across a fall in canal or river. In such powerhouses, Kaplan turbines with concrete spiral casing or tubular turbines are used for power generation. In the former case, the intake forms a part of the passage to spiral casing and this is suitably streamlined to minimise hydraulic losses. Typical layouts are shown in Fig. 2 and Fig. 3. 2.2.1.3 Forebay intakes In an open canal development, or free flow conduits terminate the open canal in a basin known in this forebay. A typical intake is shown in Fig. 4. 2.2.1.4 Drop type intake layout is provided of forebay structure, consisting of a trough trench and trash rack structure over it, is constructed across hilly streams to entrap the entire minimum discharge of the hilly stream. It is also called a trench type weir. Typical layouts are shown in Fig. 5. 2.2.1.5 power Run-of-the-river type intake for hydro- A diversion For run-of-the-river scheme power generation, intakes are provided in the dam body as is being done in case of reservoir type intake. CLOF UNIT -TRASH RACK OF ilJBE CL OF UNIT' GANTRY CRANE f RASH DRAFT RACK DISTRIBUTOR CL OF RUNNER SECTION FIG. THROUGH CL OF UNIT \RUNNER DlkMETER 2 CANAL/RIVER POWER HOUSE INTAKES ( KAPLAN TURBINES ) 2 IS 9761: 1995 MAXIMUM I II I x 1 DRAFT TUBE FIG. 3 CANAL/RIVER POWB R HOUSBINTAKES( TUBULARTURBINES) 2.3 Reservoir Type Intakes 2.3.1 Reservoir type intakes are provided where discharges for power generation are drawn from storage built up for this purpose. Depending on the head above the centre line of penstock, this is further categorised as under: a) Low head ( up to 15 m ), b) Medium head ( 15 to 30 m ), and c) High head ( above 30 m ). 2.3.1.1 Intake in concrete or masonry dams When power house is located at the toe of concrete or masonry dam and the water passage to turbine is embedded penstock through the body of dam, the intake structure for such penstocks is of semi circular type. A typical layout is shown in Fig. 6 and Fig. 7. 2.3.1.2 Re-entrant type of intake This type of intake is generally provided either at upstream face of dam or in open channel with flat bottom, the typical layout of which 1s shown in Fig. 8. 2.3.1.3 Intake in earthen dam When the reservoir is formed by an earthen dam and a conduit is laid below it, the intake structure for such layout will be a sloping intake or tower type of intake. A typical layout for sloping type intake is shown in Fig. 9 and for tower type intake in Fig. 10. 2.3.1.4 Intakes in reservoir independent of dams In the case of pressure tunnel taking off from a storage reservoir where the intake is located at a distance from the dam, the intake structure of such layout will be either tower type, semi-circular or inclined. A typical layout is shown in Fig. 11. 3 TYPICAL LAYOUT OF INTAKE STRUCTURE 3.1 The main components are: of an intake structure from a) Bellmouth entrance and transition rectangular to circular opening, b) Trash rack supporting c) Gate slot enclosures d) Antivortex breast-wall, devices etc. structure, with air vents, and such as perforated 3.1.1 The economic design of intake to serve its function will depend upon the condition in each project. In 5.1.3 and 5.1.5 some formulae have been indicated which may be modified to 3 IS 9761 : 1995 suit spa cial studies may conditions. Hydraulic conditions. be necessary under model special opening ( where B is the width of opening of the conduit ). The main features of this layout are: a> Bellmouth entrance to conduit; b) Semicircular trash rack structure; c) Gate slot enclosure with airvent ( typical details are shown in Fig. 6 ); and devices such as breast-wall, d) Antivortex etc. FOREBAY I AXIS OF INTAKE STRUCTURE 3.2 The main type of layouts are as follows. 3.2.1 Semicircular In this placed conduit within Type of Intake Structure layout, the rack supporting structure is in a semicircle plan in front of the opening so that no part of rack falls a radius of I.1428 B from the face of the APPROACH CHANNEL \ \ TRASH RACK GROOVE 4A Plan AXIS OF INTAKE STRUCTURE -t a SILT EXCLUDER PIPF 9 k i SECTION 46 Section OF INTAKE Structure STRUCTURE PENSTOCK of Intake FIG. 4 LAYOUT OF FORBBAYINTAKE 4 IS 9761 : 19% BOULDER PITCHING DRV BOULDER PITCHING SEDIMENT EXCLUDER -INTAKE CONDUIT DRY BOULDER L SELECTED BOULCER 5A Plan PITCHING OULDER PITCHING VER FILTER SCOPE AS PER SITE CONDITION SECTION 56 6 B FIG. 5 DROP TYPB INTAKE 5 -"------*-- ---- ---.---- IS 9761 : 1995 SHARP EDGE OPENING `THROUGH bp BARS ,- AIR VENT TRASH RACK SLOT-, -CL OF PEN STOCK APRON- FIG. 6 SEMI CIRCULAR TYPE INTAKESTRUCTURB 3.2.4 Tower Type of Intake Structure 3.2.2 Re-entrant Type Intake ( see Fig. 8 ) 3.2.3 Straight Type of Intake Structure In this layout, the rack supporting structure is straight with a vertical or inclined face. Where mechanical rakes with guides are provided, the trash rack should be kept inclined at an angle of at least 15" to the vertical. The main features of this layout are: a) Bellmouth transition: b) Vertical or inclined trash rack structure at the face of transition or away from the face; C) Gate slot enclosure with air vent ( typical details are shown in Fig. 12 ); and d) Antivortex devices such as breast-wall, etc. 6 Tower type of intake structure is a circular vertical shaft. The main features are: a) Circular tower structure; type rack supporting b) Circular bellmouth to shaft; c) Vertical shaft below tower supporting structure; and type rack d) Bend from shaft to tunnel with optional accelerating elbow and flare, depending on model studies. The flow into tower is generally controlled either by a single cylinderical gate or by a number of gates in the tower type intake structure as shown in Fig. 10. IS 9761:1995 SECTION x _x FIG. EDGE0 FACE OF SHARP CIRCULAR ORI 7 SBMICIRCULAR TYPE INTAKB c) Type of water conductor tunnel, canal or penstock; system, that is, INE OF ORIFICES IFlCE d) Topographical features of area; e) Ii1 cases where there is a considerable movement of boulders, stones and sand in the down stream direction, the intake should be arranged so that the effect of such movement will not lead to a partial restriction or blockage of the intake; in respect of storage reservoir intakes the sill level of the intake should be aimed to be kept above the sedimentation level at or near the dam face arrived at; and f) The intake can often be located so as to enable it to be constructed before the level of the reservoir is raised. 4.2 The typical layouts classified in 3.2.1 to X2.4, are adopted for a particular work based on requirements governed by prevailing condition. Conditions suitable for various layouts are given in 4.2.1 to 4.2.4. Sectional FIG. Plan of Intake TYPB 4.2.1 Semicircular Type of Intake Structure is adopted: 8 PENSTOCK INTAKE RB-ENTRANT This type of layout 4 CONDITIONS FOR LOCATION AND LAYOUT OF IN%AKE STRUCTURE 4.1 The structure choice depends of location upon: of the intake a) Type of development, that is, run-of-theriver or storage dam project; b) Location dam ; of power house vis-a-vis the is formed by a high a) when a reservoir concrete or masonry dam and penstock conduit laid in the body of the dam; and geology permit b) when the topography to have almost vertical face to tunnel inlet portals; and depth of water above c) when the minimum the centre line is more than 0.8 of the entrance height ( he ). 7 IS 9761 : 1995 PRESSURE TUNNEL GATE ARRANGEMENT FIG. 9 SLOPING INTAKEFOR AN EARTH DAM TRASM RAC PIERS FIG. 10 TOWER TYPE INTAKB 4.2.2 Re-entrant Type Intake This type of layout is adopted: a) 011 upstream b) when the intake is subjected to low head variations like in run-of-the-river type. 4.2.4 Tower Type of Intake Structure This type of layout is adopted: a) when the intake is located at a distance from the upstream face of the dam; is formed by the b) when the reservoir earthen dam and penstock tunnel is laid below it; and c) when the intake is subjected to large head variations, resulting in complete submergence of structure. 8 face of dam; b) in open channel with flat bottom; and to c) where the width of dam is inadequate accommodate the intake. 4.2.3 Straight Type of Intake Structure This type of layout is adopted: a) when the reservoir is formed by earthen dam and conduit is laid below it; and IS 9761 : 1995 GANTRY CRAMnm TRASti RACK . . STEEL LINER . . . . . ., I , . I FIG. 11 INTAKE IN RESERVOIR INDEPENDENT OF DAMS END OF TRANSITION TRASH RACK FIG. 12 STRAIGHT TYPE INTAKE IS 9761: 1995 5 HYDRAULIC DESIGN OF COMPONENTS OF INTAKE 5.1 Bellmouth Opening and Transition 5.1.1 Shape and Size of Opening The penstock and conduit entrance should be designed to produce an acceleration similar to that found in a jet issuing from a sharp edged orifice. The surface should be formed to natural contraction curve and the penstock or conduit is assumed to be the size of orifice jet at its maximum contraction. 5.1.2 The normal contraction of 40 percent ( C, = 0.6 ) should be used in high and medium head installations, 30 percent ( C, = 0.7 ) for installations and 50 percent head low ( C, = 0.5 ) for re-entrant type intake. 5.1.3 Opening Area Opening where dc;= angle of inclination of penstock centre line to horizontal; and co-efficient of contraction, as defined in 5.1.2. Area Penstock Area c, cos r#l 5.1.4 Height and Width of Opening The height above and centre line Fig. 13 for for details hr is calculated from the distance below the intersect of the penstock with the face of the entrance ( see lower and upper nappe and Fig. 14 of side-flaring entry in plan ). 7 )rj2 + 1.1 tan $ ] D [( I.21 tans 4 + 0.084 1 2cos+ h2 = D 0.79 1 ~0s + 0.077 tan 4 he = h -+ h, Width 5.1.5 of opening b, = Area he >I - of opening Shape of Opening The inlet should be streamlined to minimize the losses. The profile of the roof and floor should approximate to that of a jet from the horizontal slot. The profile is ge.nerally an ellipse given by the following equation: (1.1 X4 D)" + Y2 (0.291 D)" ' NOTE - Hydraulic Model Studies may be conducted for important structures. TRANSITION /.__./ "pkN%tc by0.2113b, r a; "`+-Y'=, b,2 =' 90.554 \ b, _____-M________ L/____ b, t FIG. 13 BELLMOUTH DETAILS FOR LOWER AND UPPER NAPPE 10 1S 9761 : 1995 GATE GROOVE -, I FIG. 14 DETAIL OF (SIDB FLARING) ENTRY IN PLAN 5.1.6 The profile of sides should be such that it should generally be followed by equation: ( O*&_ )a + -(&;-b$p= ' approach geometry, flow conditions, velocity at the intake, geometrical features of trash rack submergence depth and structure relative withdrawal Froude number, etc. The geometry of the approach to the power intake should be such that it can ensure economy, and better hydraulic uniform flow condition. The flow lines should be parallel, having no return flow zone and having no stagnation. Velocity distribution in front of penstock should be uniform. 5.2.2 To prevent vortices, the centre line of intake should be so located as to ensure submergence requirements given in Fig. 18 which has been developed by an evaluation of minimum design submergence at prototypes operating satisfactorily. For large size intakes at power plants: While providing side flarings it may be ensured that the size of opening at entry does not create any structural problem with the size of dam block or structure. In case the dam block or structure in which the intake is to be accommodated has restrictions, the dimensions of side flaring should be restricted to that extent. NOTE - Hydraulic Model Studies may be conducted for important structures. 5.1.7 Transitions In order to obtain hydraulically efficient design of intake transitions from rectangular section to a circular section conduit, the transition should be designed in accordance with the following requirements: ( F, - - V +' @ 6 113 > Transition or turns should be made about the centre line of mass flow and should be gradual, Side walls should not expand at a rate greater than 5" from the centre line of mass flow, All slots or other necessary departures from the neat outline should normally be outside the transition zone. 5.2 Centre Line of Intake 5.2.1 especially at pumped submergence depth, storage system, height a or h = 1 to I.5 times the intake diameter is recommended. For medium and small size installations ( F, > l/3 ), especially at pump sumps, submergence requrrements may be calculated using the formula: h D - - 0.5 + 2 F, Formation of vortices at the intake depends on a number of factors such as The recommendattons are valid for intakes with proper approach flow conditions. With well 11 IS 9761 : 1995 controlled approach flow conditions, with a suitable dimensioning and location of the intake relative to its surroundings and with use of antivortex devices submergence requirements may be reduced below the limits recommended above. However, recourse to hydraulic model studies may be taken to determine more accurate value depending on the specific parameters of the particular structure. PENSTOCK \ , 5.2.3 The requirement of water cover may be of anti-vortex reduced with the provision devices such as: a) Parallel vertical fins of R.C.C. on the upstream face of the power dam. Typical layout is shown in Fig. 15. b) Dinorwic louvered type. is shown in Fig. 16. c) Perforated breast-wall. shown in Fig. 17. 5.3 Trash Rack Structure A in front entrance through runner. 5.3.1 Typical layout is Typical layout I RESERVOIR INTAKE LA FIG. 15 ANTI VORTBX DEVICE (PARALLEL FINS) AT THE RESERVOIR INTAKE trash rack structure should be provided of a penstock or conduit to prevent the of any trash that would not pass easily the smallest opening in the turbine 5.3.2 The shape of trash rack structure may be adopted to meet the requirements of the headworks layout and head loss. For instance, for high dams with nearly vertical upstream face, semi-circular trash rack structure is usually preferred to provide the required trash rack area economically. For low dams or diversion structures, a straight trash rack is usually preferred. However, model studies required for suitability of shape and size of piers and beams of trash racks should also aim at to prevent dead zones of water and uneven or irregular flow patterns in the tunnel, formation of dimples, dye core and aircore vortices, water circulation and other flow irregularities during operation in pumping, turbine or combine modes under symmetrical and asymmetrical operation of unit. 5.3.3 No part of the trash rack structure should fall within 80 percent of the intake height, he, from the centre point of intake. 5.3.4 For an upright semicircular intake structure ( as in Fig. 6 ), the racks should be located on a semicircle in plan with a minimum radius of l-142 8 b, where be is the width of opening. For an inclined semicircular intake structure ( as in Fig. 7 ), the racks should be located or; a semicircle or a plane perpendicular to the axis of the structure and satisfying the other criteria 12 PENSTOCK FIG. 16 DINORWIC TYPE ANTI VORTBX Dsvrcs AT POWER INTAKE IS 9761 : 1995 5.3.6 The normal rack structure velocity of flow through is indicated below: the For units with hand raking, V = 0.75 m/s For units with mechanical raking r PERFORATEb WALLS WITH I BREAST 20% OPENINGS V = 1.5 m/s 5.3.7 Trash bars should net opening between least 5 mm less than between turbine runner be so spaced that the them should be at the minimum opening blades. 5.3.8 The trash rack should also be designed to withstand the effect of submerged jets in the case of pumped storage scheme. The spacing of the bars should be adjusted so that the ratio of forcing frequency to natural frequency of bar is less than 0.6. 5.3.9 For the design of trash rack piers, ribs and trash rack screens, a minimum differential head of 3-6 m may be adopted depending upon the efficiency of the cleaning of trash racks being adopted. RESERVOIR NTAKE A AA L FIG. 17 ANTI VORTEX DEVICE (PERFORATED BREAST-WALL) AT THE RBSBRVOXR INTAKE For the design of perforated breast-wall, antivortex louvers and vertical fins, a minimum of 1 m differential head may be adopted. as for the upright structure. In plane the racks would be laid out on an ellipse, the semi-major axis of which should have a minimum value of: 1,142 8 b, I___-_ cos 9 where 0 is the inclination of the trash rack axis to the vertical. The semi minor axis of the structure is parallel to the dam face and would have a value of I.142 8 b,. The trash rack screens should be inclined in a three dimensional plane with a bottom corner of the tower screens resting over the base footing. Suitable fillet should be provided below the lowest screens to plug the gap and effectively support the weight of the trash rack over the entire base. For shaft intakes ( as in Fig. 10 ), the racks should be located at O-8 D1 from the centre of the bellmouth, where D, is the inlet diameter of the bellmouth. 5.3.5 The piers and beams of the trash rack supporting structure should be sharp nosed and should be streamlined about the required structural section. 13 min 2 1DI 1 1, 1rr.r (1.3 , 0.5 . 1.0 1.5 2.0 I - Fr laroe size intahescd+medium and small size installafor-power plants, ' tions, e. g. , all kinds of outlet especially pumped control structures, intakes at storage systems Lavigation locks, diversion lm/s -v-3m/s tunnels and water supply reser(mean value : Pm/s) voirs cooling water inlets and especially pump intakes 2m/s v - 6mis ( mean value : 4mls 1 FIG. 18 RECOMMBNDEDSUBMERGBNCE FOR INTAKBS WITH PROPBR APPROACH FLOW CONDITION BUT WITHOUT USE OF SPBCIAL DEVICES FOR VORTEX SUPPRBSSION 5.4 Intake Gate and Air Vent 5.4.1 The intake gate slot should be enclosed in a structure designed to guide the water into rectangular the opening without side contraction. 5.4.2 The upstream edge of the gate slot should be at least 0.40 b, from the nose, where b, is the width of opening. 5.4.3 Where gates are located in a gate shaft, suitable transition from circular to rectangular gate slot should be provided. 5.4.4 An air vent downstream of intake gate should be provided. The air vent should be so designed as to admit air at the rate the turbine is discharging water under full gate conditions. The area of air vent following formula: F- c = co-efficient of discharge through inlet ( 0.5 for ordinary type of intake valves and 0.7 for short air inlet pipes ). 5.5 Approach Apron The approach apron should not be placed closer than 30 percent of the intake height h, from the lower edge of the intake orifice. 6 MISCELLANEOUS ARRANGEMENT 6.1 Whenever the intakes are provided at high altitude above snow line, necessary provision for arresting the formation of ice cover on rack bars and gate should be made for the free flow of water. These de-icing arrangements are as under: a) Bubbler system, and b) Heating arrangement. 6.2 Floating ice should be arrested by providing ice booms of concrete baffles at intakes. 6.3 Raking Arrangement may be fixed by the Q 2/ s( D/t )3/a 750 oooe where e".Area of air vent pipe in ma, Maximum discharge through penstock. Discharge of air through pen-stock is taken as 21 to 22 percent of penstock discharge, factor of safety against collapse of pipe ( normally assumed between 3 and 4 ), diameter of penstack s- Arrangement should be made for removing debris from trash racks at regular intervals or with continuous raking arrangements in the case of intake where floating material is expected to be attracted continuously to the racks due to the abundance of floating material in the flow and the level of water being often near about trash rack levels. 6,4 In the case of run-of-the-river type projects, where the requirements of silt exclusion are more stringent, separate arrangements should be made for silt exclusion. D Z t= : thickness of penstick in m, in m, and Bursro of Indian Standards BIS is a statutory institution established under the Bureau of Indian Stundurdr Act, 1986 to promote harmonious development of the activities of standardization, marking and quality certification of goods and attending to connected matters in the country. Copyright No part of these publications may be reproduced in any BIS has the copyright of all its publications. form without the prior permission in writing of BIS. This does not preclude the free use, in the course of implementing the standard, of necessary details, such as symbols and sizes, type or grade designations. Enquiries relating to copyright be addressed to the Director ( Publications ), BIS. Review of Indian Standards Amendments are issued to standards as the need arises on the basis of comments. 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